The present invention relates to a method for controlling an actuator of a vehicle transmission. The invention also relates to a corresponding computer program, computer readable medium, control unit, and vehicle transmission. The invention is applicable on vehicles, in particularly heavy duty vehicles such as e.g. trucks or working machines. However, although the invention will mainly be described in relation to a truck, the invention is of course also applicable for other type of vehicles, such as e.g. cars or buses, etc.
In relation to vehicle transmissions, for example, transmissions used in heavy duty vehicles such as trucks or buses etc., an automated manual transmission is often utilized. The automated manual transmission changes gear automatically such that gear and specific time of changing gear is executed automatically. It is common and well known to execute a gear shift when the gears are synchronized, i.e. the relative speed between the engaging sleeve and the gear to be engaged are approximately zero. However, in some applications non-synchronized gear shift occurs and in these applications it is of great importance to control the gear shift such as to achieve a reduction of unwanted noise as well as to reduce dynamic loads.
Prior art solutions provides a method for executing a non-synchronous gear shift in a vehicle transmission by supplying a force on the engaging sleeve such that the engaging sleeve is forced in a direction towards the gear wheel to be engaged. The engaging sleeve thereafter reaches the gearwheel to be engaged whereby gear shift occurs. However, this method for shifting gear is often associated with the provision of high dynamic loads and unwanted noise when the engaging sleeve hits the gear to be engaged in the axial direction thereof. The dynamic loads may, if they are too severe, result in a reduction of gearbox component durability, as well as to negatively affect gearbox electronics due to shock loads resulting from the dynamic loads.
There is thus a need to provide a method for executing non-synchronized gear shift in a vehicle transmission that reduces associated dynamic loads and hence provides for increased durability of transmission components.
It is desirable to provide a method which reduces the dynamic loads and unwanted noise when executing a gear shift in a vehicle transmission.
According to a first aspect of the invention, there is provided a method for controlling an actuator of a vehicle transmission, the actuator being connected to an engaging sleeve, the engaging sleeve being axially displaceable between a gear wheel disengaging position and a gear wheel engaging position of the vehicle transmission for executing a transmission gear shift, wherein the method comprises the steps of actuating the actuator during a first predetermined time period for initiating a translational movement of the engaging sleeve from the gear wheel disengaging position towards the gear wheel engaging position, wherein the first predetermined time period is smaller than a total time period for the engaging sleeve to reach the gear wheel engaging position; determining, during a second time period initiated after the duration of the first time period, if the engaging sleeve has reached the gear wheel engaging position; and actuating the actuator during a third predetermined time period if it was determined that the engaging sleeve failed to reach the gear wheel engaging position during the second predetermined time period.
The wording “gear wheel disengaging position” should in the following and throughout the entire description be interpreted as a position of the engaging sleeve where the engaging sleeve is not in final meshed connection with the desired gear wheel to be engaged when executing a gear shift. The gear wheel disengaging position may thus be a position where the engaging sleeve is in no connection to any gear wheel, i.e. a neutral position, or it may be a position where the engaging sleeve is in meshed connection to a gear wheel, but which gear wheel is not the gear wheel that is to be engaged after execution of the gear shift is completed. For example, when executing a gear shift from a first gear to a second gear, the engaging sleeve may in the initial state, before gear shift has been initiated, be in meshed connection to a first gearwheel. When the gear shift thereafter has been initiated and executed, the engaging sleeve is in meshed connection to a second gear wheel. In this example scenario, the meshed connection between the engaging sleeve and the first gear wheel should thus be interpreted as the gear wheel disengaging position even though the engaging sleeve in it self is in an engaging position to a gear wheel. Likewise and according to the above example scenario, the gear wheel engaging position should thus be interpreted as the position when the engaging sleeve is in final meshed connection with the second gear heel, i.e. when the gear shift has been executed and is completed.
Furthermore, the first predetermined time period and the second predetermined time period should be interpreted as two separate time periods. Hence, the second predetermined time period should be interpreted as a time period which is initiated after the first predetermined time period is finished. It should hence be understood that the actuator is not actuated during the second time period. The actuator is thus disengaged, or deactivated, during the second time period. It should also be understood that the duration of each of the predetermined time periods may be different depending on the specific application or prerequisites of the vehicle. For example, the first predetermined time period may have shorter time duration if the vehicle transmission is operated in a normal operating temperature in comparison to executing the method before normal operating temperature is achieved. Outside air temperature is another parameter affecting the time duration of the first predetermined time period.
Still further, already available transmission sensors may be utilized to determine whether the engaging sleeve is in the engaging position or not.
The present invention is based on the insight that by actuating the actuator for a short first predetermined time period, in order to initiate the translational movement of the actuator towards the gear wheel engaging position, will be sufficient to transport the engaging sleeve to the gear wheel engaging position. However, if the teeth of the engaging sleeve will, for example, hit the teeth of the gear wheel to be engaged during the predetermined second time period, the forces on the engaging sleeve directing the engaging sleeve towards the engaging position will eventually be reduced to limits that will not be able to fully engage the engaging sleeve when the teeth of the engaging sleeve is no longer in connection with the teeth of the gear wheel. The invention is thus also based on the insight that further actuation of the actuator should be executed if it is determined that the engaging sleeve has not reached the gear wheel engaging position during the second predetermined time period, such that an axial force is provided to the engaging sleeve to enable the engaging sleeve to be engaged.
The advantages of the present invention is that the dynamic loads when the teeth of the engaging sleeve hit the teeth of the gear wheel to be engaged, in the axial direction, will be reduced in comparison to actuating the actuator during the complete cycle from a disengaged position to an engaged position of the engaging sleeve. According to an example embodiment, the method may further comprise the consecutive step of actuating the actuator until it is determined that the engaging sleeve has reached the gearwheel engaging position if the engaging sleeve failed to reach the gear wheel engaging position within a predetermined maximum allowable time period.
Hereby, the actuator provides a force on the engaging sleeve until it is fully engaged, in order to execute the gear shift during a reasonable time limit. An advantage is that a forced gear shift is provided if it is determined that further provision of actuating pulses will not complete the gear shift until an excessive time period has lapsed. However, it should be readily understood that further actuating pulses could be provided to the actuator after the above described third predetermined time period and before the predetermined maximum allowable time period has lapsed.
According to an example embodiment, the method may further comprise the step of rotating the engaging sleeve around an axially extending geometric axis relative to a gear wheel to be engaged if the engaging sleeve failed to reach the gear wheel engaging position within the predetermined maximum allowable time period.
An advantage is that further provision for positioning the engaging sleeve in the gear wheel engaging position is provided. Hereby, if the engaging sleeve is stuck in a position where the edge of the teeth of the engaging sleeve is in contact with the edge of the teeth of the gearwheel to be engaged, a rotation of the engaging sleeve in relation to the gear wheel to be engage may enable the engaging sleeve to be further directed to the gear wheel engaging position. This may be advantageously combined with the above described example embodiment of actuating the actuator until the engaging sleeve is engaged.
According to an example embodiment, the first time period may end when teeth of the engaging sleeve collide with teeth of a gearwheel to which the engaging sleeve is to be connected.
Hereby, a preset and well defined time period is provided. Also, actuating the actuator until the teeth of the engaging sleeve hit the teeth of the gear wheel to which the engaging sleeve is to be engaged may provide an actuating pulse which is sufficient for further directing the engaging sleeve to the gear wheel engaging position after the teeth of the engaging sleeve is aligned with the root of the gear wheel.
According to an example embodiment, the actuator may be a pneumatic cylinder comprising a shift rod connected to the engaging sleeve.
A pneumatic cylinder is easy to handle and can utilize an already available air/gas pressure supply tank of the vehicle to which the transmission is provided. Other types of actuators are of course conceivable, such as e.g. a hydraulic actuator or an electrically controlled actuator.
According to an example embodiment, the pneumatic cylinder may be controlled by means of at least one valve arranged in fluid communication between the pneumatic cylinder and an air pressure supply tank.
The wording “fluid communication” should be understood to include communication by means of air/gas. Hence, the wording “fluid communication” should include an air/gas communication between the pneumatic cylinder and the air pressure supply tank.
An advantage is that the valves are easy to control and can thus be connected to a control unit that determines when to open and close the valve such that the actuator is actuated/deactivated.
According to an example embodiment, the time periods for actuating the pneumatic cylinder may be controlled by means of positioning the at least one valve in an open state such that pressurized air is supplied from the air pressure supply tank to the pneumatic cylinder.
According to an example embodiment, the transmission gear shift may be a non-synchronized gear shift.
A non-synchronized gear shift should be interpreted as a gear shift where the rotational speed of the engaging sleeve is not synchronized with the rotational speed of the gear wheel to which the engaging sleeve is to be engaged. Advantages of a non-synchronized gear shift is that less components are required in comparison to a synchronized gear shift, arrangement, since e.g. a traditional synchromesh unit is not needed. Also, the components generally have a lower weight. Hence, the non-synchronized gear is cheaper than a synchronized gear shift arrangement.
According to a second aspect of the present invention, there is provided a computer program comprising program code means for performing any of the above described steps in relation to the first aspect of the present invention when the program is run on a computer. According to an example, the computer may be an embedded realtime system.
According to a third aspect of the present invention, there is provided a computer readable medium carrying a computer program comprising program code means for performing any of the above described steps in relation to the first aspect of the present invention when the computer program is run on a computer. According to an example, the computer may be an embedded real-time system.
According to a fourth aspect of the present invention, there is provided a control unit connectable to a vehicle transmission comprising an actuator connected to an engaging sleeve, wherein the engaging sleeve is axially displaceable between a gear wheel disengaging position and a gearwheel engaging position of the vehicle transmission, wherein the control unit is configured to actuate the actuator during a first predetermined time period for initiating a translational movement of the engaging sleeve from the gear wheel disengaging position towards the gearwheel engaging position, wherein the first predetermined time period is smaller than a total time period for the engaging sleeve to reach the gearwheel engaging position; determine, during a second time period initiated after the duration of the first time period, if the engaging sleeve has reached the gear wheel engaging position; and actuate the actuator during a third predetermined tinge period if it was determined that the engaging sleeve failed to reach the gear wheel engaging position during the second predetermined time period.
According to an example embodiment, the vehicle transmission may further comprise at least one valve arranged in fluid communication with the actuator, wherein the control unit is connected to the at least one valve and configured to control the valve to be positioned in an open state or a closed state.
According to a fifth aspect of the present invention, there is provided a vehicle transmission comprising a control unit as described in relation to the fourth aspect of the present invention. According to an example embodiment, the transmission may be an automated manual transmission.
Effects and features of the second, third, fourth, and fifth aspects of the present invention are similar to those described above in relation to the first aspect of the present invention.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing frond the scope of the present invention.